Kwolek died Wednesday in Talleyville, Delaware following a brief illness, said her friend, Rita Vasta, who is handling Kwolek's affairs. She was 90.

Kwolek had no remaining family, Vasta said.

"We are all saddened at the passing of DuPont scientist Stephanie Kwolek, a creative and determined chemist and a true pioneer for women in science," DuPont CEO Ellen Kullman said in a written statement Thursday. "Her synthesis of the first liquid crystal polymer and the invention of DuPont Kevlar highlighted a distinguished career."

Kwolek developed Kevlar, a substance five times stronger than steel, by spinning fiber from a liquid crystalline solution. Kevlar's lightweight, durable qualities have made it a long-lived material used in body armor and other protection equipment used by police and the military.

The discovery came in the mid-1960s when Kwolek was 42, working at DuPont's Experimental Station outside of Wilmington to develop a super-strong fiber to reinforce radial tires.

She invented a solution of rigid-chain polymers that fell from her lab spatula like water. The substance was much thinner than most polymers, and when put into a machine could be spun into strong, stiff material.

Stephanie Kwolek (left) speaks to members of the Delaware Academy of Chemical Sciences at a luncheon in 2007. At right is former Delaware Gov. Russell W. Peterson, who died in 2011.(Photo: Special to The News Journal/JOHN RANDOLPH)

She told The News Journal in 2007 that DuPont management "didn't fool around. They immediately assigned a whole group to work on different aspects. ... It was very exciting, let me tell you."

Kevlar's use over time broadened to other applications, including sporting equipment, as it minimizes vibration and can bend without shattering. DuPont recently agreed to serve as a sponsor of the ESPN X Games, where sporting equipment makes liberal use of Kevlar. DuPont will celebrate Kevlar's 50th anniversary next year.

News of Kwolek's death came a day after DuPont Protection Technologies announced that a million bullet-resistant vests have been sold using DuPont Kevlar XP since that version of the product was launched in 2008. Today, most police agencies have adopted mandatory vest requirements.

"When you think about what she has done, it's incredible. There's literally thousands and thousands of people alive because of her," said Ron McBride, former manager of the Kevlar Survivors' Club, a not-for-profit partnership between DuPont and the International Association of Chiefs of Police. The group has documented 3,200 lives saved through use of Kevlar in body armor.

McBride is a former chief of police in Ashland, Kentucky. A vest with Kevlar saved the life of his son, who was serving as a naval operative in Iraq.

"She could look back on her life and say, 'Yeah, I made a difference,' " he said.

Kwolek held just a bachelor's degree from the institution that preceded Carnegie Mellon University in Pittsburgh when she joined DuPont as a chemist in 1946.

Coming from humble roots, and having studied in a one-room schoolhouse, she found an opportunity at DuPont because many men were in the military at the time.

"She was stubborn, she clung on, and she did the work because she found it interesting," said Caroline Angel Burke, project manager at the Museum of Science in Boston, which chose Kwolek as one of a handful of engineers featured in a permanent exhibit.

Kwolek, who stood just 4 feet 11 inches tall, never married.

"In those days for chemists, when you're hot on the trail of something, there's not a lot of time to go dating," Vasta said. "She loved outdoor sports, she had plenty of friends, she socialized. But when it came to lab work, that was 100 percent of her focus."

Stephanie Kwolek at work in 1967 in the DuPont Co. Pioneering Research Lab at the Experimental Station, preparing a polymerization experiment.
(Photo:
Courtesy of DuPont
)

Vasta, who counted Kwolek as a mentor when they both worked at DuPont in the 1980s, said Kwolek continued to develop Kevlar over the years before her retirement in 1986. She went on to mentor women who wanted to go into the sciences, Vasta said.

Kwolek got a nice lab at DuPont after the discovery, but recognized she was in the company of many other distinguished scientists, Vasta said. Kwolek always said that DuPont compensated her properly for her discovery, Vasta said.

In the 2007 interview, Kwolek was careful to take credit only for the initial discovery of the technology used in the development of Kevlar, crediting the team for taking it further, especially DuPont scientist Herbert Blades.

Kwolek was proud whenever first responders approached her to tell her that her vest saved their life, Vasta said.

In 1996, Kwolek won the National Medal of Technology "for her contributions to the discovery, development and liquid crystal processing of high-performance aramid fibers, which provide new products worldwide to save lives and benefit humankind." She was only the third DuPont scientist to win a National Medal of Technology or Science, Kullman said.

"She leaves a wonderful legacy of thousands of lives saved and countless injuries prevented by products made possible by her discovery," Kullman said.

In Kwolek's later years, she enjoyed being in her home, Vasta said. She left behind her lab notebooks, and "oh my gosh, they're like literary pieces," she said, noting her fluid handwriting and sketches.

Kwolek was inducted into the the Hall of Fame of Delaware Women on March 27.

Kwolek kept spools of Kevlar fabric at her home, she told The News Journal in 2007. "I never in a thousand years expected that little liquid crystal to develop into what it did," she said.